A catheter serving as a stent delivery system is just one example of a medical device with a distal end that is advanced into the body through a percutaneous puncture. The distal end advances in the body transluminally. Often, the lumen is part of the cardiovascular system, but not necessarily. In one very common procedure, known as the Seldinger technique, catheters are introduced into the cardiovascular system through a puncture point in the thigh of the patient.
As stent delivery catheter devices become more sophisticated, they have become more compact, in cross-sectional areas. The normal unit of dimension to designate cross-sectional areas is the unit of length called “French” which is ⅓ of a millimeter. Thus, a “Six-French” catheter has an outside diameter of two millimeters.
With increasing diameter, the demands on tissue at the point of entry to the body, and the risk of leakage of blood at that entry point, tend to increase. Typically, a catheter is introduced at the point of entry of the body through an introducer sleeve which extends from outside the body, through the puncture point, into the lumen of interest, to provide a path along which the distal end of the catheter can advance through the percutaneous puncture and into the desired lumen. However, the provision of such an introducer sleeve increases the diameter required, at the point of entry to the body. Self-evidently, doing without any introducer sleeve would be one way to reduce the total diameter needed, at the point of entry. Indeed, some doctors are responding to tissue difficulties at the point of entry by performing the catheter introduction without any introducer sleeve. While this reduces the total diameter requirement, it brings disadvantages, specifically, that the abluminal surface of the catheter moves longitudinally, proximally and distally, against the bodily tissue at the point of entry, tending to increase the likelihood of loss of blood at that entry point.
An elongate medical device that is advanced transluminally within the body of a patient usually has a distal end that is to perform some sort of medically advantageous function within the body, such as deploying a stent. Normally, the shaft serves as a link between the proximal and distal ends of the device but does not have to perform a medical procedure in its own right, so it can be slimmer. The present invention is particularly adapted to medical devices in which the maximum cross-section of the distal end of the device is greater than the maximum cross-sectional area of the shaft portion. For examples of medical devices featuring a distal tip that is somewhat thicker than its shaft, reference is made to EP-A-1025813 and U.S. Pat. No. 5,772,669.
In order to reduce the leakage of blood through the entry point, often referred to as “backbleed”, the use of an additional sleeve placed around the catheter shaft has been suggested in U.S. Pat. No. 5,203,774. This sleeve is slidably arranged on the catheter shaft so that it can be axially displaced with respect to the catheter and has a distal end for being introduced into the inner lumen of an introducer sleeve. A flange with a diameter that is larger than that of said distal end is provided at a proximal end of the sleeve. The flange engages over the edges of the introducer sleeve so as to prevent the sleeve from being axially displaced. Such an arrangement allows the catheter shaft to be freely advanced and retracted with respect to the sleeve partly positioned in the introducer sleeve but reduces backbleed that, in the absence of the sleeve, may occur through the gap between the inner lumen of the introducer sleeve and the catheter shaft. A similar sleeve configuration is also disclosed in U.S. Pat. No. 5,836,306 and U.S. Pat. No. 5,334,160.
The sleeve arrangements described in the above-referenced documents ought to reduce the occurrence of backbleed, in particular with respect to the length of constant external diameter of the shaft of the catheter as it is introduced into a patient's body. These sleeves are configured to be disposed within a proximal portion of an introducer sleeve and prevented from any further distal movement in an axial direction of the catheter shaft by a proximal sleeve portion, such as a flange, that has an outer diameter larger than the inner diameter of the proximal introducer sleeve portion. Hence, the length along which the medical device can be introduced into a patient's body is limited to the length of the catheter shaft which can advance through the sleeve. Specifically, if the catheter were to have a thicker proximal shaft portion which has an outer diameter larger than the inner diameter of the sleeve, then such a proximal portion would have to remain at all times proximal of the backbleed-preventing introducer sleeve.
In peripheral vascular procedures, the distance between the point of bodily entry and the site of surgical treatment within the body can widely vary and may not be known precisely in advance of the procedure.
FR-A-2 625 897 discloses a conically shaped plug element that is slidably disposed around the tube of a medical probe. After the probe has been introduced into the blood vessel of a patient, the plug element is arranged and fixed within the entry point of the vessel so as to tightly seal it. When inserted in the entry point, the plug element exerts a pressure on the probe tube that is sufficient to prevent it from moving in an axial direction of the probe. In this way, the probe is immobilised in a desired position with respect to the blood vessel.